lock and insert formula in a cell based on selection of text in another cell

I am having an issue on Excel. I have a drop down menu in cell D5, with three options, A, B, and C.

If A is to be selected, cell content in D6 should become zero/clear-out [i.e., available for manual input by user], and cells D7, D8 and D9 should be locked while having formulas assigned to them as follows: for D7, =D6*G9, for D8 = D6*G10, for D9 = D6*G11

Similarly, if B is to be selected, cell content in D7 should become zero or clear-out, and cells D6, D8 and D9 should be locked while having the following formulas assigned to them for D6 = D7*G8, for D8 = D6*G10, for D9 = D6*G11

And lastly, if C is to be selected, cell content in D8 and D9 to be zeroed out and available for user input, while cells D6 and D7 are locked out and have following formula assigned to them: D6=(D8+D9)*I9, D7= D6*G9

I am completely novice on VBA in Excel and clueless as to how to solve this issue.

I got a code by googling which helps me to lock out cells, but I have no idea how to blank out cells and assign formulas.

The issue is, if I just type in the formula, lets say in D6, and user selects option A in dropdown, he will have option to overwrite value in D6 and later on if option B or C is chosen, D6 will remain static instead of moving in line with the values input in D7-D9 when options B/C are chosen.

Can someone please help

Walekum Salaam
Naveed, you are a life saver... thank you so much!!!
I could hug you right now!!!

Salaams Naveed
Follow-up question. If I need to do the same thing in two columns of the sheet, column D is already done, what to do for Column E. I suppose simply copy pasting the code below in the VBA window and replacing D to E won't really work.
All the logic remains same, just need to duplicate same settings on column E to have two columns have these properties.